The Industrial Raspberry Pi Forum

Hello,

I want to connect an potentiometric displacement sensor like https://www.burster.com//en/displacemen ... /8712-8713 to the AIO module. This is basically a big potention meter, however the data sheet of the sensor clearly states that using the sensor as a voltage divider should be avoided.

The sensor itself doesn't supply power so it should be also coming from the AIO, which I think shouldn't be a problem.

In short the AIO sends out 10V goes through the sensor and reads back what is left, hence is knows the position of the sensor.

The question is, when I use 0 - 10V Analog Input how much current is flowing? The data sheet of the sensor advices I < 0.1 μA Is this doable with the AIO module?

Hi Edbo,

sorry for late reply.
Do I understand you in the right way?

• You want to use that Potentiometer ? With which resistance?
  • measuring range 10 mm and 25 mm 1 kΩ
  • measuring range 50 mm up to 150 mm 5 kΩ

• Do you want to use an analog output of the RevPi AIO as supply for your sensor?

• You dont want use a voltage divider, because it is recommended by the datasheet ? Where did you find this comment, because i did not find that in the datasheet. Just this Important: The excellent characteristics of these sensors are only evident when the slider current is < 0.1 μA. If the measuring chain requires higher currents, it is recommended to use an operational amplifier connected as a voltage follower (I < 0.1 μA).

• Please attach a drawing of your idea to wiring your sensor with our AIO

According to our datasheet AIO, the AIO has following input impedance

• Voltage >900 kΩ

• Current <250 Ω

After you answer my question, I think we can help you much better.

Best regards,
Johannes

->Johannes<- wrote: ↑12 Feb 2021, 14:49

• You want to use that Potentiometer ? With which resistance?
  • measuring range 10 mm and 25 mm 1 kΩ
  • measuring range 50 mm up to 150 mm 5 kΩ

I want to use the 5k version.

->Johannes<- wrote: ↑12 Feb 2021, 14:49

• Do you want to use an analog output of the RevPi AIO as supply for your sensor?

I need a stable voltage source like +5V or +10V, so I was thinking to get it from the AIO module (no need to have an extra supply and it kind of closes the circuit). But a separate supply is also possible.

->Johannes<- wrote: ↑12 Feb 2021, 14:49

• You dont want use a voltage divider, because it is recommended by the datasheet ? Where did you find this comment, because i did not find that in the datasheet. Just this Important: The excellent characteristics of these sensors are only evident when the slider current is < 0.1 μA. If the measuring chain requires higher currents, it is recommended to use an operational amplifier connected as a voltage follower (I < 0.1 μA).

I was not very clear . In principle the sensor IS a voltage divider, but it is recommend to keep the current as low as possible. Because the sensor is directly connected to an input pin of the AIO module, the input impedance should almost go to infinity. Hence they mentioned an opamp.

->Johannes<- wrote: ↑12 Feb 2021, 14:49 According to our datasheet AIO, the AIO has following input impedance

• Voltage >900 kΩ

Calculating the current with 10V gives a current of 0.0111 mA which is 11μA. This goes down when using 5V. This is also a maximum and way below the maximum current of 10 mA in the circuit (according the datasheet).

I have to dig a bit deeper myself and do some small tests on my breadboard, but it should be possible to use the AIO for this sensor.

Hi Edbo,

ok, then dig
It would be nice, if you share your test and measurement results with us.
I am curious about it.

Best regards,
Johannes

Unfortunately the customer did chose another path forward so I'm not going to put more time into this. That said, you should be able to connect things up like https://duino4projects.com/analog-input-using-arduino/. Even it's for an Arduino, you can replace that with the AIO (I don't have one, so it's a wild guess). It would be nice if the AIO was able to supply the voltage as well.